1. Field of the Invention
This invention relates to emergency exit door latches, and more particularly, this invention relates to exterior locks and operators for emergency exit door latches.
2. Background of the Invention
It is frequently desirable to provide emergency exit doors with latching means that can be locked and unlocked from the outside so that access can be selectively controlled from the outside while egress remains unaffected or can be controlled from the inside.
U.S. Pat. application Ser. No. 22,110, filed Mar. 20, 1979, discloses an emergency exit door latching and locking apparatus which includes a closure retracted latch bolt that is dogged in the projected position by a toggle linkage. When the toggle linkage is pushed over-center by a panic bar, the bolt is undogged and the door will open when pushed upon. In U.S. Pat. No. 22,110, the toggle linkage is connected to a hydraulic delay which retards retraction of the bolt so as to hold the person trying to gain egress at the door for a predetermined period of time as an alarm rings. If there is an emergency situation, the hydraulic circuit loading the toggle linkage is opened by de-energizing a solenoid which closes a normally open valve in the circuit, thereby permitting immediate retraction of the bolt and opening of the door.
The emergency exit door lock and latch disclosed in U.S. Pat. No. 22,110 cannot be operated or opened from the outside because prior to the invention which is the subject of that patent application, the particular problem of operating such a lock and latch from the outside did not exist. There are additional considerations which must be taken into account due to the delay means, such as, deactivation of the delay circuit and selective deactivation of the alarm.